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Production of macromolecular activators of phagocytosis by lysed platelets
1Third Department of Medicine, Kagawa Medical University, Kita-gun, Japan.
Abstract:
Macromolecular activators of phagocytosis from platelets (MAPP: 1-MAPP and s-MAPP) are released from activated fresh platelets and enhance leukocyte phagocytosis via the Fcgamma receptors. In this study, production of MAPP was investigated in lysate of freeze-thawed stored platelets (PL). Incubation of PL and thrombin with precursors of MAPP (pre-MAPP: pre-1-MAPP and pre-s-MAPP) produced 1-MAPP and s-MAPP, whereas products released from stored platelets by stimulation with thrombin or collagen did not produce MAPP after incubation with pre-MAPP. The action of thrombin in MAPP formation with PL and pre-MAPP was inhibited by antithrombin III and heparin, and sequential incubation studies indicated that the key site of action of thrombin was on a component of PL. Other serine proteases such as trypsin could be substituted for thrombin in this reaction, whereas the action of thrombin was specific when whole platelets were used instead of PL. Gel filtration of PL before and after treatment with thrombin suggested that a macromolecule in PL (PMA-I) is digested by thrombin and liberates a 700 to 800 Da substance (PMA-II) which converts pre-MAPP to MAPP.
Insights
Stored platelets can produce macromolecular activators of phagocytosis (MAPP) when treated with thrombin. This process involves thrombin-mediated digestion of a platelet component, yielding a substance that converts MAPP precursors into active MAPP.
Area of Science:
- Immunology
- Hematology
- Biochemistry
Background:
- Macromolecular activators of phagocytosis (MAPP) from fresh platelets enhance leukocyte phagocytosis via Fcgamma receptors.
- Understanding MAPP production from stored platelets is crucial for potential therapeutic applications.
Purpose of the Study:
- To investigate the production of MAPP from stored, freeze-thawed platelets (PL).
- To elucidate the mechanism of MAPP formation involving thrombin and platelet components.
Main Methods:
- Incubation of PL with thrombin and MAPP precursors (pre-MAPP).
- Assessing MAPP production under various conditions, including inhibition studies with antithrombin III and heparin.
- Gel filtration of PL before and after thrombin treatment to identify involved macromolecules.
Main Results:
- Thrombin treatment of PL with pre-MAPP successfully produced MAPP.
- MAPP production was inhibited by antithrombin III and heparin, indicating thrombin's role on a PL component.
- Thrombin digestion of a platelet macromolecule (PMA-I) released a substance (PMA-II) that converts pre-MAPP to MAPP.
Conclusions:
- Stored platelets can be induced to produce MAPP via thrombin-mediated processing.
- A specific thrombin-sensitive macromolecule in platelets (PMA-I) is key to generating the MAPP-activating substance (PMA-II).
- This finding offers insights into MAPP generation from platelet stores for immunological applications.